Method for manufacturing a membrane electrode assembly

Abstract

To provide a manufacturing method of a membrane / electrode assembly, capable of improving the quality of the membrane / electrode assembly.SOLUTION: A manufacturing method of a membrane / electrode assembly containing: a polymer electrolyte 11; and a pair of electrodes 12 and 13 provided while nipping the polymer electrolyte, where the electrode contains a catalyst layer 14 bonded to the polymer electrolyte; and a gas diffusion layer 15 bonded to the catalyst layer, comprises: a step of bonding a catalyst layer support body 102 and the catalyst layer by contacting the catalyst layer support body made of a sublimable material and the catalyst layer; a step of bonding the polymer electrolyte and the catalyst layer by contacting the catalyst layer bonded to the catalyst layer support body to the polymer electrolyte; and a step of sublimating the catalyst layer support body bonded to the catalyst layer in a state where the polymer electrolyte and the catalyst layer are bonded.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a membrane electrode assembly. [Background technology]

[0002] A membrane electrode assembly (MEA) used in a fuel cell is manufactured by joining an electrode layer consisting of a catalyst layer and a gas diffusion layer to an electrolyte membrane.

[0003] Patent Document 1 discloses a method for producing a membrane electrode assembly in which a catalyst layer and a gas diffusion layer are formed on an electrolyte membrane, and then the gas diffusion layer is pressed from the outside. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-216789 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional methods using a pressing process, it is difficult to ensure the flatness of the catalyst layer due to the uneven shape of the gas diffusion layer made of carbon paper, etc. Furthermore, the pressing process can damage the catalyst layer and electrolyte membrane, making cross-leakage more likely to occur if the electrolyte membrane is thin.

[0006] Furthermore, if the ionomer is added after the catalyst layer has been applied onto the gas diffusion layer, the ionomer may permeate the gas diffusion layer, resulting in a deterioration in the gas diffusion performance of the gas diffusion layer. Furthermore, it becomes difficult to control the amount of ionomer retained in the catalyst layer to an optimum amount.

[0007] In view of the above, an object of the present invention is to provide a method for manufacturing a membrane electrode assembly that can improve the quality of the membrane electrode assembly. [Means for solving the problem]

[0008] To achieve the above object, claim 1 provides a method for manufacturing a membrane electrode assembly, comprising the steps of joining a catalyst layer support and a catalyst layer, joining an electrolyte membrane and a catalyst layer, and sublimating the catalyst layer support.

[0009] The membrane electrode assembly includes an electrolyte membrane (11) and a pair of electrodes (12, 13) sandwiching the electrolyte membrane, and the electrodes include a catalyst layer (14) bonded to the electrolyte membrane and a gas diffusion layer (15) bonded to the catalyst layer. In the step of bonding the catalyst layer support to the catalyst layer, the catalyst layer is brought into contact with a catalyst layer support (102) made of a sublimable material. In the step of bonding the electrolyte membrane to the catalyst layer, the catalyst layer bonded to the catalyst layer support is brought into contact with the electrolyte membrane. In the step of sublimating the catalyst layer support, the catalyst layer support is sublimated while the electrolyte membrane and the catalyst layer are bonded together.

[0010] According to the present invention, a catalyst layer is formed using a catalyst layer support made of a sublimable material, thereby obtaining a free-standing single-layer catalyst layer. This allows the catalyst layer to be transferred to the electrolyte membrane without a pressing step, making it possible to produce a membrane electrode assembly that is not dependent on the shape of the gas diffusion layer. As a result, the flatness of the catalyst layer can be improved, damage to the electrolyte membrane can be avoided, and the quality of the membrane electrode assembly can be improved.

[0011] The reference numerals in parentheses for the above components indicate the corresponding relationship with the specific means described in the embodiments to be described later. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a conceptual diagram showing a membrane electrode assembly according to an embodiment of the present invention. [Figure 2] 1A to 1C are diagrams illustrating a manufacturing process of a membrane electrode assembly. [Figure 3] FIG. 2 is a diagram showing a CV curve of a membrane electrode assembly according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. A membrane electrode assembly 10 of this embodiment is a membrane electrode assembly (MEA) for a fuel cell, and is particularly used in a phosphoric acid fuel cell that uses phosphoric acid as the electrolyte.

[0014] As shown in Fig. 1, the membrane electrode assembly 10 includes an electrolyte membrane 11 and a pair of electrodes 12, 13 sandwiching the electrolyte membrane 11. The pair of electrodes 12, 13 comprises an anode 12 and a cathode 13. The anode 12 is also called a hydrogen electrode, and the cathode 13 is also called an air electrode.

[0015] The membrane electrode assembly 10 constitutes a fuel cell that outputs electrical energy by utilizing an electrochemical reaction between hydrogen and oxygen in the air. A fuel cell made up of the membrane electrode assembly 10 is used as a basic unit, and multiple sheets can be stacked to form a stack structure.

[0016] When hydrogen is supplied as a fuel gas to the anode 12 and air is supplied as an oxidant gas to the cathode 13, the hydrogen and oxygen undergo an electrochemical reaction to output electrical energy, as shown below.

[0017] (Anode side) H2 → 2H + +2e - (Cathode side) 2H + +1 / 2O2+2e - →H2O At this time, hydrogen is converted into electrons (e - ) and protons (H + ), and the protons move through the electrolyte membrane 11. Meanwhile, at the cathode 13, a catalytic reaction occurs to generate water (H2O) from the protons that have moved from the anode 12, electrons that have circulated from the outside, and oxygen (O2) in the air.

[0018] The membrane electrode assembly 10 of this embodiment generates electricity without humidifying the electrolyte membrane 11. In other words, dry air is supplied to the cathode 13 during operation of the membrane electrode assembly 10. This allows the membrane electrode assembly 10 to generate electricity at temperatures of 100°C or higher.

[0019] The electrolyte membrane 11 has a configuration in which an electrolyte retention material is impregnated with phosphoric acid. In this embodiment, polybenzimidazole (PBI) doped with phosphoric acid is used as the electrolyte membrane 11. Phosphoric acid is a proton conductor.

[0020] The anode 12 and the cathode 13 have the same configuration. The anode 12 and the cathode 13 each include a catalyst layer 14 disposed in close contact with the electrolyte membrane 11 and a gas diffusion layer 15 disposed on the outer side of the catalyst layer 14. The catalyst layer 14 is bonded to the electrolyte membrane 11, and the gas diffusion layer 15 is bonded to the catalyst layer 14.

[0021] The catalyst layer 14 includes catalyst-supported carbon 14a and ionomer 14b that coats the catalyst-supported carbon 14a. The catalyst-supported carbon 14a is composed of a carbon support and catalyst particles supported on the carbon support. In this embodiment, Pt particles are used as the catalyst particles in the anode electrode, and PtCo particles are used in the cathode electrode. The ionomer 14b is a proton conductor, and in this embodiment, phosphoric acid is used.

[0022] A conductive porous material is used for the gas diffusion layer 15. In this embodiment, the gas diffusion layer 15 is made of a porous carbon material such as carbon paper or carbon cloth.

[0023] Next, a method for manufacturing the membrane electrode assembly 10 of this embodiment will be described. In the method for manufacturing the membrane electrode assembly 10 of this embodiment, a sublimable material is used as the catalyst layer support 102 when transferring the catalyst layer 14 to the electrolyte membrane 11. The sublimable material is a material that changes directly from a solid phase to a gas phase at room temperature and evaporates.

[0024] Examples of sublimable materials that can be used include parasol (paradichlorobenzene), naphthalene, and camphor. The melting point of parasol is 53.5°C, that of naphthalene is 80.3°C, and that of camphor is 180°C. The sublimable material used for the catalyst layer support 102 may be selected taking into consideration its compatibility with the catalyst layer 14 and the electrolyte membrane 11, its melting point, and the like. In this embodiment, parasol, which has a low melting point and is easy to handle, is used as the sublimable material.

[0025] The method for manufacturing the membrane electrode assembly 10 will be described below in order with reference to Fig. 2. In Fig. 2, the manufacturing steps proceed in order from (1) to (7).

[0026] First, as shown in (1), a step of preparing the catalyst layer 14 is carried out.

[0027] In this process, catalyst-supported carbon is spray-coated onto the polyimide film 100 to form the catalyst layer 14, and a sintering process is performed in which the polyimide film 100 is heated to 350°C in a reducing atmosphere for one hour. The sintering process removes the binder contained in the catalyst layer 14. The polyimide film 100 is a material with excellent smoothness and heat resistance, and is used as a base for the catalyst layer 14. The base for the catalyst layer 14 may be a material different from the polyimide film 100, as long as it is a material with excellent smoothness and heat resistance.

[0028] Thereafter, the polyimide film 100 and the catalyst layer 14 are cut into 10 mm square pieces, thereby obtaining a bonded body of the catalyst layer 14 and the polyimide film 100.

[0029] Next, as shown in (2), a step of preparing a catalyst layer support 102 is carried out.

[0030] In this process, parasol powder is sprinkled on a PET film 101 placed on a slide glass (not shown), and the film is heated to 70°C on a hot plate to melt the parasol. This forms a catalyst layer support 102 on the PET film 101. The PET film 101 is used as a material with excellent smoothness and peelability.

[0031] Next, as shown in (3), the catalyst layer 14 is brought into contact with the catalyst layer support 102, and the catalyst layer support 102 and the catalyst layer 14 are joined together.

[0032] In this step, the assembly of the catalyst layer 14 and the polyimide film 100 is placed on the molten catalyst layer support 102 so that the catalyst layer 14 is in contact with the catalyst layer support 102. At this time, the molten catalyst layer support 102 penetrates into the catalyst layer 14, improving the adhesion between the catalyst layer support 102 and the catalyst layer 14 and increasing the contact area between the catalyst layer support 102 and the catalyst layer 14.

[0033] After it is confirmed that the catalyst layer 14 has adhered to the molten catalyst layer support 102, the heating by the hot plate is stopped and the catalyst layer support 102 is slowly cooled. By slowly cooling the catalyst layer support 102, the transfer rate of the catalyst layer 14 to the catalyst layer support 102 when peeling the polyimide film 100 from the catalyst layer 14 can be made higher than in the case of rapid cooling.

[0034] Next, as shown in (4), a step of peeling off the polyimide film 100 and the PET film 101 from the assembly of the catalyst layer support 102 and the catalyst layer 14 is carried out.

[0035] In this step, the catalyst layer support 102 is slowly cooled, and then the polyimide film 100 is peeled off from the catalyst layer 14. The polyimide film 100 can be peeled off from a corner using tweezers. Next, the PET film 101 is peeled off from the catalyst layer support 102. This makes it possible to obtain a bonded body of the catalyst layer 14 and the catalyst layer support 102, and a self-supporting single-layer catalyst layer 14.

[0036] Next, as shown in (5), a step of adding an ionomer 14b to the catalyst layer 14 is carried out.

[0037] In this step, with the catalyst layer 14 facing upward, ionomer 14b diluted with ethanol is dropped onto the surface of the catalyst layer 14 and dried. In this embodiment, phosphoric acid is used as the ionomer 14b. Because water-diluted ionomer 14b does not penetrate into the catalyst layer 14 and is repelled by the surface, it is desirable to use ionomer 14b diluted with ethanol.

[0038] Next, as shown in (6), the catalyst layer 14 and the catalyst layer support 102 are brought into contact with each other, and the assembly of the catalyst layer 14 and the catalyst layer support 102 is bonded to the electrolyte membrane 11.

[0039] In this step, the electrolyte membrane 11 is attached to a slide glass 103, and an assembly of the catalyst layer 14 and the catalyst layer support 102 is placed on the electrolyte membrane 11 so that the catalyst layer 14 faces the electrolyte membrane 11. This bonds the catalyst layer 14 to the electrolyte membrane 11. In this embodiment, the electrolyte membrane 11 is made of polybenzimidazole doped with phosphoric acid.

[0040] Next, as shown in (7), a step of sublimating the catalyst layer support 102 is carried out.

[0041] In this step, the catalyst layer 14 and the electrolyte membrane 11 are left in a bonded state at room temperature for a day and a night. As a result, the catalyst layer support 102 made of a sublimable substance sublimes and disappears, and the catalyst layer 14 can be transferred to the electrolyte membrane 11.

[0042] Through the above steps, an assembly is completed in which the catalyst layer 14 is bonded to one side of the electrolyte membrane 11. A catalyst layer 14 can also be bonded to the other side of the electrolyte membrane 11 by performing the above steps. The membrane electrode assembly 10 is completed by attaching gas diffusion layers 15 to the outside of the catalyst layers 14 bonded to both sides of the electrolyte membrane 11.

[0043] Next, the results of measuring the membrane electrode assembly 10 of this embodiment by cyclic voltammetry will be described with reference to Fig. 3. Fig. 3 shows a CV curve of the membrane electrode assembly 10 of this embodiment.

[0044] The membrane electrode assembly 10 of this embodiment is manufactured without using a pressing process. The membrane electrode assembly 10 of this embodiment uses phosphoric acid as an ionomer at 0.5 μL / cm 2 is added.

[0045] As shown in Fig. 3, the CV curve of this embodiment does not show an increase in current with increasing voltage. Therefore, it was concluded that cross leakage does not occur in the membrane electrode assembly 10 of this embodiment. Furthermore, no significant effect was observed on the ECSA (effective platinum utilization area).

[0046] According to the present embodiment described above, the catalyst layer 14 is formed using the catalyst layer support 102 made of a sublimable material, thereby obtaining a self-supporting single-layer catalyst layer 14. This allows the catalyst layer 14 to be transferred to the electrolyte membrane 11 without a pressing step, making it possible to manufacture a membrane electrode assembly 10 that is not dependent on the shape of the gas diffusion layer 15. As a result, the flatness of the catalyst layer 14 can be improved, damage to the electrolyte membrane 11 can be avoided, and the quality of the membrane electrode assembly 10 can be improved.

[0047] In this embodiment, the catalyst layer 14 is formed on the molten catalyst layer support 102, and the molten catalyst layer support 102 can penetrate into the catalyst layer 14. This improves the adhesion between the catalyst layer support 102 and the catalyst layer 14, making it possible to increase the contact area between the catalyst layer support 102 and the catalyst layer 14, and making it easy to obtain a self-supporting single-layer catalyst layer 14.

[0048] Furthermore, when peeling off the catalyst layer support 102 from the catalyst layer 14 after bonding the catalyst layer 14 to the electrolyte membrane 11, the adhesion between the electrolyte membrane 11 and the catalyst layer 14 must be higher than the adhesion between the catalyst layer 14 and the catalyst layer support 102. In contrast, in this embodiment, the catalyst layer support 102 is made of a sublimable material, and by sublimating the catalyst layer support 102, problems associated with peeling do not occur.

[0049] Furthermore, in this embodiment, the catalyst layer 14 can be transferred to the electrolyte membrane 11 without performing a pressing process, so that even if the electrolyte membrane 11 is made thin, the occurrence of cross leakage can be suppressed.

[0050] Furthermore, in this embodiment, the catalyst layer 14 can be transferred to the electrolyte membrane 11 without performing a pressing process, so that the ionomer 14b added to the catalyst layer 14 can be prevented from permeating into the gas diffusion layer 15, thereby preventing a decrease in gas diffusion performance.

[0051] Furthermore, if the ionomer 14b is dripped onto the catalyst layer 14 while the catalyst layer 14 is bonded to the gas diffusion layer 15, the ionomer 14b may permeate the gas diffusion layer 15. In contrast, in the present embodiment, the ionomer 14b can be dripped onto the catalyst layer 14 while the catalyst layer 14 is not bonded to the gas diffusion layer 15, making it easier to control the amount of the ionomer 14b dripped.

[0052] In this embodiment, polybenzimidazole is used as the electrolyte membrane 11. Polybenzimidazole is a material on which it is difficult to directly form the catalyst layer 14 by spray coating or the like. In contrast, according to the manufacturing method of this embodiment, the catalyst layer 14 can be easily formed on the electrolyte membrane 11 using polybenzimidazole.

[0053] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications can be made as follows without departing from the spirit of the present invention. Furthermore, the means disclosed in each of the above-described embodiments may be combined as appropriate within the scope of feasibility.

[0054] For example, in the above embodiment, the ionomer 14b is added in step (5) after the catalyst layer 14 is formed on the catalyst layer support 102. However, if the sintering process of heating the catalyst layer 14 is not performed in step (1), a step of adding the ionomer 14b to the catalyst layer 14 may be performed in advance before the catalyst layer 14 is formed on the catalyst layer support 102.

[0055] Furthermore, in the above embodiment, the assembly of the catalyst layer 14 and the catalyst layer support 102 is arranged so that the catalyst layer 14 faces the electrolyte membrane 11, but this is not limiting, and the assembly of the catalyst layer 14 and the catalyst layer support 102 may be arranged so that the catalyst layer support 102 faces the electrolyte membrane 11. [Explanation of symbols]

[0056] 10 Membrane electrode assembly 11 Electrolyte membrane 12, 13 electrodes 14 Catalyst layer 14b Ionoma 15 Gas diffusion layer 102 Catalyst layer support

Claims

1. A method for producing a membrane electrode assembly, comprising an electrolyte membrane (11) and a pair of electrodes (12, 13) sandwiching the electrolyte membrane, the electrodes including a catalyst layer (14) bonded to the electrolyte membrane and a gas diffusion layer (15) bonded to the catalyst layer, A step of contacting a catalyst layer support (102) made of a sublimable material with the catalyst layer to bond the catalyst layer support and the catalyst layer; a step of bringing the catalyst layer bonded to the catalyst layer support into contact with the electrolyte membrane to bond the electrolyte membrane to the catalyst layer; sublimating the catalyst layer support in a state where the electrolyte membrane and the catalyst layer are bonded together; A method for manufacturing a membrane electrode assembly comprising:

2. The method for producing a membrane electrode assembly according to claim 1, further comprising the step of adding an ionomer to the catalyst layer.

3. 3. The method for producing a membrane electrode assembly according to claim 1, wherein in the step of joining the catalyst layer support and the catalyst layer, the catalyst layer support is brought into contact with a molten catalyst layer.

4. 4. The method for producing a membrane electrode assembly according to claim 1, wherein the sublimable material is any one of naphthalene, paradichlorobenzene, and camphor.

5. 5. The method for producing a membrane electrode assembly according to claim 1, wherein the electrolyte membrane is made of polybenzimidazole.

6. 6. The method for producing a membrane electrode assembly according to claim 1, wherein the electrolyte membrane contains phosphoric acid, and the phosphoric acid serves as a proton conductor.

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